Description: While I was teaching a class a couple of years ago, I got some photos of a phenomenon that I think is very cool and under appreciated. The top photo is an early stage embryo of the starfish Pisaster ochraceus (32 hrs old, cultured at about 10-12°C). At this stage, the blastula stage, the embryo consists of a single layer of cells in a ball. Most of the embryos in this batch were very wrinkled, with irregular, deep folds and creases, and irregular patches of cells inside the epithelium. Yet, after 2 days, most of the embryos had formed very regular gastrula-stage embryos (bottom image): the creases and wrinkles were gone. (Note, the tube poking inside the embryo is the archenteron, which will become the gut. It's not related to the folds and creases. I've embedded a video I made, scanning through a gastrula-stage embryo to give a sense of its 3D structure, just because I like it.)
I think it's fascinating that starfish embryos can pass through this very irregular stage and clean themselves up. Not all of them do it, and in some species some batches of embryos become wrinkly and others don't, and they apparently form wrinkled embryos more frequently when cultured in low salinity seawater (Kobayakawa and Satoh 1978), which suggest some clues to what causes it.
Early development involves lots of cell-cell signalling. How do they manage it correctly when the folds bring different patches of cells together in different ways in different embryos? Also, given that the folds don't always occur, it seems like there must be a lot of mechanical variation among embryos. If this is the case, how do they manage to do the shape changes of gastrulation (which form the archenteron) despite that variation? How much mechanical variation is there really?
We cultured these embryos for my class, so we only had the one batch, and I was too busy to keep as careful track as I'd like of the conditions.
The reference above is to: Kobayakawa Y and Satoh N 1978 Induction of the wrinkled blastula formation in the starfish, Asterina pectinifera, by modified developmental conditions Biol. Bull. 155 150–60
Page creator's name: Mickey von Dassow
Page creator's contact info: Via IGoR contact page.
Created: 21 Dec 2014 23:21
Updated: 06 Jan 2015 21:36